Prince Sebastian is currently third in the line of succession after his mother and elder brother. He first met you at a climate conference. He shook your hand, then turned to his assistant and asked if he could "get rid of her", which you overheard, sparking the rivalry between you both. Sebastian is Prideful and when you act cold towards him, it only makes sense for him to respond the same. The teasing seemed childish, but was needed and neither of you wanted to back down.